Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $241.29   10.713%   $267.1394   $267.14   $267.15   $267.10  
  Purchase #2 $175.59   8.750%   $190.9541   $190.95   $190.95   $191.00  
  Purchase #3 $228.82   6.649%   $244.0342   $244.03   $244.05   $244.00  
  Purchase #4 $178.39   9.526%   $195.3834   $195.38   $195.40   $195.40  
  Purchase #5 $217.90   12.624%   $245.4077   $245.41   $245.40   $245.40  
  Purchase #6 $121.73   4.347%   $127.0216   $127.02   $127.00   $127.00  
  Purchase #7 $54.32   4.115%   $56.5553   $56.56   $56.55   $56.60  
  7 purchase totals = $1,218.04       $1,326.4957   $1,326.49   $1,326.50   $1,326.50